This invention relates to electromagnetic plunger pumps, and more particularly it is concerned with an automatic air venting device for an electromagnetic plunger pump suitable for use with an electromagnetic plunger pump when the latter is used with a gun type burner, for example, in which the pump delivering small quantities, such as an electromagnetic plunger pump, that has a relatively large number of strokes of the plunger per unit hour with a small length of the strokes operates to draw by suction volatile fuel oil, such as kerosene, light oil, etc., from a fuel tank located in a lower position than the position in which the pump is located, to feed such fuel under pressure and eject it in atomized particles for combustion.
The air venting device according to the invention has particular utility when used with a pump of what is generally referred to as the free piston type, such as an electromagnetic plunger pump to be described in the explanation of the embodiment of the invention, which has a plunger supported between two springs for reciprocatory movement as subsequently to be described in detail whose strokes have their lengths automatically varied by the pressure of the fluid, flow resistance and whether the springs are compressive or noncompressive.
In this type of pump, when the aforesaid fuel oil is drawn by suction from a fuel tank located in a position lower than the position of the pump and fed under pressure to a combustion system, such as boiler, hot water feeding system, heater, etc., to eject the fuel in atomized particles through a nozzle for combustion, there has arisen a problem that the phenomenon of what is referred to as vapor lock occurs due to vaporization of the fuel caused by the suction negative pressure of the pump when the residual air in the fuel is separated or when the fuel oil flows through a feed line. One example of piping involved in this phenomenon will be described by referring to FIG. 1. Fuel oil 106 in a fuel tank 105 is drawn by suction, as a pump 101 is actuated, through a suction line 103 and a strainer 102 by opening an ON-OFF valve 104. The fuel oil 106 flows through a discharge line 107 and is ejected from a nozzle 108 of a combustor in atomized particles ignited by an ignition coil, not shown, of the spark ignition type, so that combustion takes place in the combustor. In this type of combustion system, the suction head of the pump is over 2 meters and sometimes reaches several meters and the horizontal distance of the piping between the pump 101 and the fuel tank 105 exceeds ten meters. Moreover, the suction line 103 has a relatively large inner diameter and usually pipes of 3/8" are used in many cases. Thus in some cases, the suction line 103 has a large internal volume with a diameter of over 10 mm or a diameter of 1/2" in the case of steel pipes. On the other hand, in this type of pump, the discharge plunger is small in diameter and cross-sectional area and has a very short stroke, so that the volume of fluid delivered by each stroke is very small and volume efficiency is low. When the pump has to cope with compressive fluid, such as air, or fuel in a gaseous state produced by vaporization of the liquid fuel, the pump is low in efficiency because it merely repeats expansion and compression thereof. Particularly when the fuel oil fills the discharge line up to an orifice of a small diameter, such as the nozzle, on the discharge side of the pump, it takes time for the pump to remove air and gasified fuel therefrom. This gives rise to what is referred to as vapor lock in and between the suction valve, pressure chamber and discharge valve, rendering the pump inoperative because the supply of fuel oil is blocked. When this phenomenon occurs, it takes time to restore the pump to its normal operating condition, so that the pump of the aforesaid suction conditions can be hardly put to practical use. When a trap 110 of the inverted U shape is connected to the piping to keep clear of an obstacle to piping between the fuel tank and the pump, the aforesaid gas tends to stagnate in this portion of the piping and its volume gradually increases until it suddently separates itself from this portion of the piping and enters the suction side of the pump to cause vapor lock to occur, thereby interfering with the operation of the pump.
When the suction line has a great length as aforesaid, difficulties presently to be described have been experienced. In case the fuel in the fuel tank has been consumed and the tank has to be replenished or the oil in the fuel tank is drawn therefrom for the first time, the suction line is filled with air which must be removed by drawing before the fuel oil can be drawn by suction. To this end, an air vent valve is mounted on the discharge side of the pump which is opened before the pump is started. Also, when vapor lock occurs due to collection of gas in the suction line during operation of the pump, the air vent valve must be opened manually to vent air from the suction line.
To avoid these difficulties when this type of electromagnetic plunger pump is utilized for feeding fuel oil in atomized particles to the combustor, various requirements have had to be met. These requirements include minimization of the suction head, minimization of the horizontal distance between the pump and the fuel tank and limitation of the inner diameter of the suction line to a value in the range between 4 and 6 mm. Unless these requirements are met, trouble has often occurred in the operation of the pump.